that series of previews did more to turn me off 4e sight unseen than any competitor could have. And they charged money for the privilege. Thank the gods above and below that I was not one of their suckers.
We've had this conversation before, and maybe it's a mistake to rehash it, but I'm a sucker . . .
Worlds and Monsters is, in my view, one of the best GMing books published for a mainstream RPG. The 4e DMG would be significantly better if most of its advice on adventure and campaign design was dropped, and replaced by the contents of W&M.
One of the strengths of the 4e DMG is that it gives advice on how to design a combat encounter not from the perspective of ingame reality and likelihoods, but from the metagame perspective of a GM trying to put together a fun game.
W&M has the same sort of advice, only rather than being addressed to combat encounter design, it talks about the way using different sorts of creatures and world/story elements contributes to a fun game. The only analogue to this sort of discussion in the actual DMG is its discussion of langugaes, which explains, from the metagame point of view, why their are only 10 languages and how the GM is expected to use languages in the game. (Contrast the Monster Manuals, which contain lots of fiction about the monsters - ie the relevant story material - but don't have anything at the metagame level that advised the GM on how to
use this fiction in the context of setting up and running a game.)
For those who think that 4e suffers from being focused excessively on combat, I would expect that including big chunks of W&M in the DMG would significantly improve the game. Because it would make it clear that when designing a fun game, the GM can usefully think not only about the tactical elements of encounter and scenario design, but about the story elements also.
If so, then they succeeded. And there had been a whole lot of goodwill to start with. 
